The fact that electronics manufacturers are constantly introducing new products despite the economic downturn is good news to mold manufacturers who serve this industry.
One moldmaker—who is known for its specialty niche of micro moldmaking—has realized huge success by capitalizing on the recent trend of the miniaturization of electronics. the country’s only vertically integrated moldmaker and molder that exclusively specializes in micro molds
Mold manufacturers wishing to cash in on this drive toward the miniaturization of devices in a variety of industries—including electronics—need to know that micro molding is not the same as macro molding “only smaller.” Macro molding is the process of molding anything that is big—or anything that is larger than what’s considered micro molding. For the purposes of this article, micro molding is defined as once a device, component or product shrinks to the point of weighing just fractions of a gram or measuring less than 0.040 in. at the widest point, micro molding techniques are required.
For electronics manufacturers, the successful application of micro molding for micro-sensors, circuit boards, clips, mountings, LED covers and packaging for discrete components has enabled them to satiate the demand for ever-smaller cell phones, digital cameras and other devices. The miniaturization of products triggers an inverse proportion of challenges.
Electronics manufacturers seeking to develop advanced new micro designs must familiarize themselves with these new parameters or face roadblocks in making their product a reality.
Tully outlines what mold manufacturers should know before they consider entering this lucrative field.
Micro molding is a specialized form of plastic injection molding for making parts on a very small scale. How small? Finished components can easily weigh less than 1 g and measure smaller than 1 mm in cross-section.
How can this help you? To understand the many benefits of micro molding for small plastic parts, we should first look at how this process differs from conventional plastic injection molding. Then we’ll be able to understand the applications it’s best suited for, especially in medicine and related diagnostic and healthcare products.
Size Matters
Plastic injection molding machines are rated by the clamping force used to hold the two halves of the mold together. Even small conventional machines have a clamping force of at least 50 tons. That’s the maximum amount of injection pressure such a machine can withstand until the mold is forced open, which causes flashing and can damage the mold tool. So operators keep the pressure below this threshold, but not much below. That’s because if the pressure is reduced too low, there won’t be enough force to fill the mold before the resin solidifies.
Can Big Machines Make Small Parts?
It’s technically possible to use a big machine to make very small parts. But it’s not a very smart choice.
Small parts use smaller molds, and these have equally small cavities, gates, and runners. Such tools, and the resulting parts that they make, are highly sensitive to fine adjustments in pressure or temperature. But larger machines are more difficult to control precisely. Relatively speaking, it’s like using a sledgehammer to make a swiss watch.
And using a large machine to make small parts is a waste of resources because they have larger barrels with a big volume of molten resin. During one cycle, only a small amount of resin is used in each shot. The remaining resin is in the barrel, staying hot for too long. This causes the resin to degrade and can ruin the part. Smaller machines avoid this problem because they have faster cycle times and shorter barrels.
Finally, bigger machines also consume more electrical power, regardless of the size of the finished part. These operating costs are then passed along to the customer, further decreasing process efficiency.
What Are The Advantages of a Micro Molding Machine?
Miniature injection molding machines, such as our Babyplast 10/12, operate at 10 tons of clamping force at most. For a product developer, these machines represent five distinct advantages when making small parts.
Mold tools are much smaller and thus less expensive, costing approximately 40% of the price of a full-sized tool.
Micro molding consumes much less raw material. This includes not the only material used to make the part but also leftover resin in the gate and runner system as well as the barrel.
Fast changeovers are aided by using an online digital database that can hold one thousand unique job set-up parameters. And it’s also easier and faster to flush old resin out of the system to prepare the machine for a different material.
Hot runner systems are used to precisely control the temperature of the mold during production.
Faster cycle times. Micro molding machines have short, compact barrels, and the gates and runners are also of short length. Therefore even multi-cavity molds can be cycled much more quickly than their larger counterparts.
Are There Challenges for Micro Molding?
There are a few areas where micro-sized parts pose a greater challenge for the molder.
Small cavities with tiny features and thin walls are harder to machine into the tool steel. That’s why we use NAK80 or H13 polished stainless steel to make small mold tools. These steels have a fine grain with a dense molecular structure so we can use our multi-axis CNC machines to make fine features with high accuracy and tight tolerances.
Resins behave differently when micro-molding compared to their full-sized counterparts. This is because resins experience high shear forces as they are forced to fill very small cavities quickly. Since sheer is closely related to resin temperature and injection pressure, it’s important to use dedicated micro-machines that can be adjusted with fine gradations to achieve optimal results.
Measuring Small Parts
Ultimately it’s not possible to make small parts reliably unless they can be measured reliably. That’s why we have advanced 3D scanners and coordinate measuring machines that we use at every critical step to constantly monitor physical dimensions. And of course, this same careful attention to detail is used to make the mold tools.
What are Micro Parts Used For?
One of the fastest-growing markets for microdevices is the medical field. Some components can be quite small but relatively simple, while others conceal great complexity in a very small space.
What’s most important is that hospitals, insurance companies, and patients are all interested in limiting as much as possible any invasive procedures inside the body. And everyone also wants to control costs.
Therefore, there is constant pressure to develop new products on a small scale that offer diagnostic and therapeutic remedies that don’t require surgery. To do this, advanced applications combine passive enclosures with sophisticated electronics, sensors, and mechanical actuators to create an entirely new class of healthcare devices.
Bone scaffolding
Some devices are injected into the bloodstream or placed under the skin where they monitor many bodily functions. Other sophisticated mini-machines might use microfluidic pumps to deliver small doses of medicine. They can be made from bioabsorbable materials that naturally dissolve inside the bloodstream, or automatically send alerts to doctors or other caregivers should any health conditions fall outside a predetermined range of values.
When it comes to micro molding or micro injection molding, many think it is standard macro molding, just smaller. However, standard injection molding processes usually do not work when parts are smaller than a pellet of resin, have thin walls or micro features. Other factors come into play including mold design and expert mold fabrication, and the materials being used.
To put size into perspective, micro molding encompasses:
Parts that are a fraction of a pellet of resin in size
Parts that weigh fractions of a gram
Parts with a wall thickness ranging from 0.001 to 0.015 in. (25 to 375 microns)
Mold core diameters less than 0.0008” (20 micron)
Parts or sub-assemblies requiring 0.002” (50 micron) tolerances or less
High length-to-thickness (L/T) aspect ratios (currently up to 400:1)
Larger parts that have micro features, thin walls, micro holes, complex geometry and/or tight tolerances
with more complicated added features, a higher complexity of the manufacturing process, tooling and equipment is required. As generally, micro moulding requires different aspects compared to conventional moulding, specific micro moulding suppliers need to heavily invest in ultimate precision mould manufacturing machines, inspection equipment, and other specific requirements for the medical industry like class 7 cleanroom. In order to properly regulate the flow of material into the mould cavity, all micro moulding tools need to be extremely exact in their tolerances and shut-off surfaces. Consequently, it’s crucial to have highly capable toolmakers who comprehend the difficulties of micro moulding and have the knowledge required to create tooling with such tiny, precise characteristics. our design team has worked on technically challenging projects, involving specialist steel selections for optical surfaces, micro machining and fast high-temperature heat transfer, localised to optimise specific micro features. For the sustainability of the clients, our moulds also achieve long life, running between 3.5s and 5s for 40 million cycles between major refurbishment.
The intricacy of process control and the difficulties of measuring, manipulating, and examining such tiny characteristics make it difficult to validate micro moulded components. Inspecting tiny parts before sending to customers is critical, and requires extremely precise metrology. For example, facilities at Micro Systems have the CNC CMM capability of 1 micron and confocal non contact measurement systems in the nanometre range for profile and surface finish measurements, or CT-Scan CAD-Compare capability to accurately and repeatedly measure features in the microns range and optical surfaces. After inspection, micro moulded parts need to be handled and packed with great care, as they are extremely small and might require specific environmental conditions for medical purposes, so traditional handling and packaging methods might not be suitable.
Due to the variety and complexity in the structure of micro moulds, along with the fast-changing moulding technology, it is more beneficial for OEMs to outsource their micro mould projects to a specialist with unique technical advantage in this respect. Especially, in the case of micro production when tolerances and details are extremely tight, in-house tooling, moulding, assembly and testing are essential, as turnkey projects with a single mould supplier increase transparency, reduce risk, minimise time and financial waste, and achieve optimised products.